PURPOSE: To correct the looseness of corner parts due to the lack of exposure by adding recessed corner parts to be adjusting fine patterns to a photomask in case of forming a photoresist pattern by the photomask.

CONSTITUTION: In case of forming a photoresist pattern 3 having rectangular windows 2a, 3a, a reference graphic 12 of a simplar pattern is drawn at first, and then fine additional graphics 13a1W13a4 are drawn on four corners of the graphic 12. Then, a photomask having the shape of an exposure part 14a is formed on the basis of the reference graphic 12. A positive type photoresist layer 3' applied to a worked body 2 on a semiconductor substrate 1 is exposed. At that time, the lack of exposure on the four corner of the exposure pattern is corrected by fine patterns 15a1W15a4 to form an objective rectangular pattern (a). When the pattern (a) is developed, a photoresist pattern 3 having accurate rectangular windows 2a, 3a can be obtained.